1. Field of the Invention
The present invention relates to a recording head for recording images with a recording element according to received data, and a device substrate for the recording head. In particular, it relates to an inkjet recording head having an electrothermal transducer generating thermal energy for ejecting ink and a drive circuit for driving the transducer, which are formed on a common substrate, and an inkjet recording apparatus including the inkjet recording head.
2. Description of the Related Art
The electrothermal transducer (heater) and its drive circuit mounted on an inkjet-type recording apparatus as a discharge energy generating element of the recording head are generally formed on the same substrate by a semiconductor process technique, as disclosed in U.S. Pat. No. 6,290,334, for example.
Recent inkjet recording apparatuses have a tendency to provide multi-color and multi-array nozzles on the head for improving the recording quality and speed.
For instance, a configuration that has been widely used is a black-ink ejection device substrate for recording text and a color-ink ejection device substrate for recording a picture and a diagram are mounted on one recording apparatus.
For another example, a recording apparatus has been widely used for achieving multi-color recording, such as 6-color or 8-color recording, and for extending a color space and improving the gradation of recorded images.
These features of recent recording apparatuses include the progress toward higher performance in recording quality and speed by mounting a recording head having a plurality of nozzle arrays.
FIG. 1 is a schematic view showing a layout of circuit blocks of a semiconductor substrate 100 (device substrate) for such an inkjet recording head and ink supply ports.
On the semiconductor substrate shown in FIG. 1, ink supply ports 101 are aligned in six lines for supplying ink.
From these ink supply ports 101, inks are supplied to the respective nozzle arrays so that the speeding up of the recording, the extension of the color space, and the improvement of the gradation are achieved in multiple colors.
In FIG. 1, the configuration within a circuit block 105 composed of drive circuits driving heater arrays and heaters is shown only for one on the left side of the ink supply ports 101, for convenience sake, so that those of five other ports are omitted. In the drive circuit block 105, heater arrays 102, each composed of a plurality of heaters arranged in a line, oppose each other with the ink supply port 101 therebetween. Also, drive circuits 103 for selectively driving individual heaters of the heater array 102 are arranged to correspond to the respective heater arrays 102. The heater array 102 and the drive circuit 103 constitute one array circuit 106. Pads 104 are arranged at end portions of the semiconductor substrate for applying power and signals to these heater and circuit blocks.
FIG. 2 schematically shows the circuit diagram and the flow of signals in the drive circuit 103 shown in FIG. 1.
Signals including time-sharing data for driving the heaters shared by time via the pads 104 as input terminals and image data are supplied to a block selection circuit 204 and a time-sharing selection circuit 205, which constitute the drive circuit, via an input circuit 202. In this example, input data is in a serial data form, and the data in the serial data form is converted into a parallel fashion with a shift register in the block selection circuit 204 or the time-sharing selection circuit 205. The image data converted into the parallel fashion is fed to a plurality of heater drive blocks 206 provided via latches through a signal conductor line.
The block selection circuit 204 has a function to select between enabling the heater drive blocks 1 to 8 (206) to be driven and not enabling (to be effective or ineffective) based on the image data. In this example, the eight heater drive blocks 206 are arranged. Part of data is fed to the shift register in the time-sharing selection circuit 205 arranged adjacent thereto. A decoder in the time-sharing selection circuit 205 has a function to output a time-sharing selection signal that sequentially switches the heater that can be driven in the heater drive block 206 by receiving the signal from the shift register.
The block selection circuit 204 and the time-sharing selection circuit 205 constitute a selection signal output circuit 203, and the heater to be driven is selected by the respective output signals. Also, the heater drive blocks 1 to 8 constitute the heater drive block array 206.
FIG. 3 shows the circuit diagram within the heater drive block and a heater array 306.
The heater drive block 206 includes MOS transistors for driving a heater 305 arranged to correspond to the heater, and heater selection circuits (AND gates) 307. The MOS transistor for driving a heater 305 has a function to switch the turning on electricity in the heater (switching transistor). A block selection circuit signal 302 and a time-sharing signal line 303 are inputted into the AND gates 307 (heater selection circuits), so that when both the two signals become active, the output of the AND gates 307 becomes active.
The block selection circuit signal 302 is an output signal from the block selection circuit 204, and the time-sharing signal line 303 is an output signal from the time-sharing selection circuit 205.
An output signal of the AND gates 307 converts the voltage amplitude of its signal into a power supply voltage (second power supply voltage) higher than a drive voltage (first power supply voltage) used from the input circuit to the heater selection circuit 307 with a level conversion circuit 304 (level conversion). The level-converted signal is applied to the gates of the switching transistors 305. Then, electric current flows through the heater array 306 connected to the switching transistors having the voltage applied across their gates from + toward − of heater power supply wiring 301.
The level conversion from the first power supply voltage into the second voltage level is for reducing the resistance of the switching transistor 305 by increasing the voltage applied to its gate so as to enable the electric current to flow through the heater with high efficiency.
FIG. 4 is a circuit block diagram showing the electrical relationship between the shift register 204 receiving image data and a decoder 205 for driving the heaters by dividing them in a predetermined unit time (time-sharing) as a time-sharing selection circuit.
FIG. 5 is a timing chart when image data is transmitted.
In the drawing, there are shown the heater arrays, each having 128 heaters, and eight heater drive blocks, each being 16 time-sharing driving blocks capable of driving eight heaters simultaneously.
The block selection circuit needs to receive 8-bit image data (the number of blocks) for turning on/off the heater drive block from the exterior. The image data is received by eight 1-bit S/R circuits 401 and eight 1-bit latch circuits 402 constituting the block selection circuit 204. The time-sharing selection circuit is composed of the four 1-bit S/R circuits 401 and the four 1-bit latch circuits 402 for receiving the image data and serially transmitted time-sharing data. The circuit is configured, so that these shift resisters are connected in series and images are sequentially transmitted by applying a clock signal (Clock), a data signal (Data), and a latch signal (Latch) so as to convert the serial signal into a parallel fashion. The image data converted into the parallel fashion is outputted from the eight latch circuits 402 constituting the block selection circuit and is individually supplied to the eight heater drive blocks 205. On the other hand, four output signals from the 1-bit latch circuit of the time-sharing selection circuit 205 are inputted into a decoder 403. The decoder 403 has four inputs and 16 outputs, and it selects an arbitrary 1-bit output among 16-bit outputs in accordance with the inputted data. The selected time sharing signal 303 is supplied to the heater drive blocks 1 to 8 in common.
The timing chart of FIG. 5 shows an example in that when one time-sharing data is transmitted.
The data is sequentially transmitted to the 8-bit block selection circuit 204 and the 4-bit time sharing selection circuit 205, which are 12-bit S/R in total, simultaneously with the rising edge of the clock signal. The data is fed to the latch circuit 402 provided at a position where the latch signal is changed from Hi to Low every 1-bit S/R, and the image data read when the latch signal is changed from Low to Hi is maintained. The latch circuit 402 herein is active at Low.
As described above, the recent recording apparatus has a tendency to provide a plurality of arrays of the recording elements on the head corresponding to multiple colors for improving recording quality and the recording speed.
To the head with a plurality of recording element arrays, data (image data and time sharing drive data) being equivalent to the number of the recording element arrays has been inputted. These data are supplied from a printer body. The recording head needs to have data input pads being equivalent to the number of the recording element arrays. In the configuration shown in FIG. 1 and having the six ink supply ports 101 and twelve nozzle arrays, twelve data input pads (data input terminals) are generally provided for data transmission.
FIG. 6 schematically shows the relationship between each array circuit 106 of the inkjet head, the inputted data signal, the clock signal, and the latch signal.
The 12 array circuits are arranged to have six pairs, each opposing each other with the one ink supply port 101 therebetween.
The array circuit, as shown in the drawing, is composed of the selection signal output circuit (shift register and decoder) and the heater drive block array.
The signal applied to the pad is fed to each array circuit via the input circuit. The latch signal and the clock signal are commonly applied to each array circuit. The image data signal is inputted by the clock to the shift register, which constitutes the block selection circuit through the pad individually provided in each array circuit, via the input circuit. In each array circuit, the individual data signals are applied simultaneously with the common clock signal so as to selectively drive an arbitrary heater every arrays.
Since especially in the inkjet recording head, the ink supply port needs to be provided on the substrate having circuits formed thereon, the arrangement of the heaters and their peripheral circuits is limited by the ink supply port. The ink supply port is formed of a through hole penetrating the substrate from the top to the bottom, so that a circuit and wiring cannot be formed at the position of the ink supply port. Hence, the array circuits are arranged in regions sandwiched between the ink supply ports, so that the array circuit is electrically independent from each other.
Therefore, the data signal for selectively driving an arbitrary heater for each array is individually applied, so that with increasing number of arrays, the number of lines of the data signal for feeding to the head from the apparatus body is increased.
The increase in the number of lines of the data signal causes adverse effects such as cost up of the printer body for producing the signal and a tendency for increasing the sizes of the head and the carriage.